A primer treatment of adherents using as an adhesion primer a less viscous solution containing solids, such as reactive low or high molecular compounds, etc., in a relatively low concentration is one of the practical surface treatments for effecting an improvement upon adhesiveness. As examples of such a primer, silane coupling agents are well known. The following three basic functions are to be expected of the foregoing primer treatment; (1) a function of enhancing the affinity of adhesives for the surface of an adherent, (2) a function of reinforcing the surface of an adherent, and (3) a function of protecting the once formed adhesion interface to heighten the durability of adhesiveness. From the standpoint of the effectiveness for those functions, especially for (2) and (3), organosilane compounds containing a (metha) acrylic group have recently enjoyed as silane coupling agent with considerable popularity. In particular, (metha)acryloxyalkylalkoxysilanes, especially .gamma.-methacryloxypropyltrimethoxysilane, are superior in respect that they can not only be used as adhesives between various resins and all kinds of inorganic materials but also make various kinds of resins moisture curable by being grafted on said resins. However, the silane coupling agents of the above-cited kind have a defect that they cannot give satisfaction in thermal resistance.